Science: Bessemer Eye

Up to about 1870 railroad rails were made of iron because the cost of
making steel in quantity was prohibitive. Then the converters invented
by Henry Bessemer got going and steel became much cheaper. In Bessemer
converterslittle changed after 70 yearsa powerful blast of air is
forced through molten pig iron as it lies in the converter's capacious
belly. The air oxidizes impurities which form a slag or pass off as
gases through the converter mouth. After the slag has formed, the steel
is poured into molds to make ingots.